1. Field of the Invention
The present invention relates to a virtual tape device used for backup in a computer device and, more specifically, to a technique which can reduce the number of startup actions in addition to reducing the power consumption of the virtual tape device.
2. Description of the Related Art
In accordance with increased data amount in computer systems, the storage capacitance thereof has become increased. This induces more and more increase in the importance in data backup. There has been developed a virtual tape device as depicted in Japanese Unexamined Patent Publication 2006-260392 (Patent Document 1), which uses, instead of a magnetic tape device, a magnetic disk device as a storage device to which the data is to be backed up. The virtual tape device is a device in which a magnetic disk is virtually used to be emulated as a magnetic tape device.
Recently, the power consumption amount has become an issue since there has been a demand to cut the operating cost (TCO). Normally, in a storage device such as a magnetic disk array device employed in the above-mentioned virtual tape device, the power consumption amount increases in proportional to the storage capacity. MAID (Massive Array of Idle Disk) technique proposed by Dirk Grunwald of University of Colorado has achieved a new-type backup system which can have advantages of both the magnetic disk device and the magnetic tape device. With this MAID technique, it is required to achieve low power consumption through stopping the magnetic disk device that is not accessed very often. The low power consumption of a magnetic disk device of a RAID structure is achieved by storage devices disclosed in Japanese Unexamined Patent Publication 2005-099971 (Patent Document 2), Japanese Unexamined Patent Publication 11-272426 (Patent Document 3), Japanese Unexamined Patent Publication 2007-241334 (Patent Document 4), and Japanese Unexamined Patent Publication 2008-102578 (Patent Document 5), for example.
Normally, when on/off operations of the power in the magnetic device are repeated, a failure rate thereof becomes increased. Therefore, in the backup system using the MAID technique, the frequency of supplying the power to the magnetic disk device is limited. More specifically, when the power is supplied to the magnetic disk device once, it is necessary to keep the on-state for a specific time without turning it off immediately.
The disk array devices depicted in Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5 employ the MAID technique. When this MAID technique is applied to the virtual tape device, the power of the corresponding magnetic disk device is turned on every time when works for a certain virtual tape, such as recognizing the volume, allotting the virtual tape, and positioning of the tape, are to be conducted.
Specifically, with the storage device depicted in Patent Document 3 in particular, when a command for data writing processing for the magnetic disk device whose power is on is outputted, the magnetic device whose power is off is started up to recopy the data stored in the magnetic disk device (power is on) to the started-up magnetic disk device by synchronizing with the execution of the data writing processing to the magnetic disk device (power is on).
Therefore, with the storage device described above, the power supplied to the magnetic disk device can be suppressed when there is no command for the writing processing. As a result, the power consumption can be reduced.
However, the storage device manages the data supposing that the reading processing as well as the writing processing is to be executed. Thus, to start up the magnetic disk device whose power is off every time when a command for the writing processing is outputted means that it is necessary to supply the power every time the magnetic dusk device is started up. Therefore, it does not necessarily result in reducing the power consumption.
Further, the started-up magnetic disk device is turned off essentially after a specific time has passed from the time at which the device is started up. Thus, the number of turning the power of the magnetic disk device on/off is increased, so that MTBF (Mean Time Between Failure) is shortened. This may shorten the product life of the storage device itself.